TUESDAY, Jan. 4 (HealthDay News) -- Common baldness could have its roots in a newly identified stem cell defect, a finding that could potentially lead to new hair-loss treatments down the road, a new study reveals.

Researchers say they discovered that a cellular malfunction short-circuits the process by which hair follicle stem cells turn into hair-producing progenitor cells. That defect, rather than any loss of stem cells themselves, sparks the onset of androgenetic alopecia, the medical term for a type of genetic hair loss that affects both men and women, they report.

In men, this hair loss is commonly known as male pattern baldness, marked by the familiar receding hairline and thinning hair on top of the head -- a condition that sometimes leads to complete baldness. In women, female-pattern hair loss causes the hair to get thinner all over but rarely leads to baldness.

The findings offer "a lot more hope that you could actually get hair to grow in a bald scalp," said study co-author Dr. George Cotsarelis, chairman of the dermatology department at the University of Pennsylvania School of Medicine Cotsarelis.

"Previously we thought the stem cells were gone, and if that was the case it would be very difficult. But because they are present it should be possible to treat," he said.

For their study, the authors collected human scalp tissue -- both bald and haired -- discarded during hair transplant procedures performed on 54 white men who were 40 to 65 years old.

A complex series of analyses revealed that bald and haired tissue contain equivalent amounts of preserved stem cells, which give rise to progenitor cells. Bald tissue, however, did not contain the normal amount of progenitor cells, suggesting a malfunction in the normal behavior of hair follicle stem cells.

"The follicles that make hair don't go away completely, but they become miniaturized, to the point where the hair they normally make to replace hair when it naturally falls out becomes microscopic and therefore invisible," Cotsarelis said.

There are still just as many stem cells in the bald scalp that can make hair as there are in the normal haired scalp, and that was an important and surprising finding, Cotsarelis said

"It caused us to ask, 'If that is the case, why isn't the hair there?'" he said. They found that the progenitor cells, which have the job of making thick hair, are in short supply when baldness occurs "because the stem cells are for some reason blocked or incapable of making these progenitor cells," he said.

Their discovery, reported Jan. 4 in the Journal of Clinical Investigation, might someday lead to new targets for treatment of baldness, which affects millions of people worldwide, they say.

"Now that we have identified the problem we can try to better understand how to get a stem cell to make and activate a progenitor cells. And then we should be able to develop new ways of treating baldness," Cotsarelis said.

Vicki Kalabokes, president and CEO of the National Alopecia Areata Foundation, concurs. (Alopecia areata is a condition that causes round patches of hair loss.)

"There's still a long road ahead here," she cautioned. "But until now it had not been proven that this sort of stem cell defect was perhaps the problem. So this could certainly open up an avenue for future explorations looking into to how to correct this defect."

However, those hoping for a treatment anytime soon will have to wait. "Taking something from the lab to the clinic often takes decades, so there's no treatment around the corner," Cotsarelis cautioned. "It's really going to take quite a while to figure this out."

More information

For more on male pattern baldness, visit the U.S. National Institutes of Health.